This invention relates to a process for producing acetic anhydride which comprises reacting methyl acetate or dimethyl ether with carbon monoxide in the presence of a catalyst and a co-catalyst.
In the prior art, the known catalysts for producing carboxylic anhydrides from carboxylic esters or ethers and carbon monoxide include the following:
(i) a catalyst comprising a noble metal belonging to Group VIII of the Periodic Table, such as rhodium, a halide and a third component as disclosed in Japanese Patent Publication (Kokoku) No. 3926/1977; Japanese Patent Publication (Kokai) No. 65709/1976 and Japanese Patent Publication (Kokai) No. 115403/1976, Japanese Patent Publication (Kokai) No. 57733/1981 and PA1 (ii) a catalyst comprising nickel or cobalt, a halide and a third component as disclosed in Japanese Patent Publication (Kokai) Nos. 59214/1979, 78814/1977 and 78815/1977 assigned to the assignee of this application, U.S. Pat. Nos. 4,002,677, 4,002,678 and 2,729,651.
However, the catalyst (i) contains expensive rhodium as shown in Hydrocarbon Processing 54, June 83 (1975).
In case of producing carboxylic anhydrides from carboxylic esters or ethers and carbon monoxide by using a rhodium catalyst, a rhodium complex has to be prevented from being reduced to metallic rhodium under a reducing atmosphere as disclosed in Chemistry and Industry 29 (5) page 376 (1975) or the rhodium component has to be prevented from being scattered from the reaction system during the operation of separating the product as disclosed in Japanese Patent Publication (Kokai) No. 90204/1978.
In Japanese Patent Publication (Kokai) No. 59214/1979 assigned to the assignee of this invention, a nickel catalyst has been proposed in place of the noble metal catalyst. However, when using the catalyst (ii) as disclosed in Japanese Patent Publication (Kokai) No. 59214/1979 and U.S. Pat. No. 2,729,651 the reaction rate is low, and the reaction conditions are severe.